The propagation of inverted Neel wall sections in a serial access memory system was proposed by L. J. Schwee in the publication "Proposal on Cross-Tie Wall and Bloch-line Propagation in Thin Magnetic Films," IEEE Transactions On Magnetics, Mag 8, #3, Pages 405-407, September 1972. Such a memory system utilizes a ferro magnetic film of approximately 81% Ni-19% Fe approximately 350 Angstroms (A) thick in which cross-tie walls can be changed to Neel walls and Neel walls can be changed to cross-tie walls by applying appropriate fields. Associated with the cross-tie walls is a section of inverted Neel wall that is bounded by a cross-tie on one end and a Bloch-line on the other end.
In such a cross-tie wall memory system, information is entered in one end of the serial access memory system by the generation of an inverted Neel wall section, formed by a cross-tie on one side and a Bloch-line on the other, that is representative of the stored binary 1 or of a non-inverted Neel wall section, (i.e., the absence of a cross-tie, Bloch-line pair) that is representative of a stored binary 0). Such information is moved or propagated along the cross-tie wall by the successive generation, and then the selective annihilation, of inverted Neel wall sections at successive memory cells along the cross-tie wall. In the L. J. Schwee U.S. Pat. No. 3,868,660 and in the publication "Cross-Tie Memory Simplified by the Use of Serrated Strips," L. J. Schwee, et al., AIP Conference Proceedings, No. 29, 21st Annual Conference on Magnetism and Magnetic Materials, 1975, published April 1976, pages 624-625, and in the publication "Cross-Tie/Bloch-Line Detection" G. J. Cosimini, et al., AIP Conference Proceedings, No. 3, 23rd Annual Conference on Magnetism and Magnetic Materials, 1978, published March 1978, pages 1828-1830, there have been published some more results of the further development of Cross-Tie Memory Systems.
In most prior art cross-tie memory systems, the magnetic film that functions as a storage medium has the property of uniaxial anisotropy provided by its easy axis induced magnetic fields, which easy axis is generated in the magnetic film during its formation in the vapor deposition process. This easy axis provides a magnetic field induced anisotropy that constrains the generation of the cross-tie wall along and parallel to the easy axis. In the above referenced L. J. Schwee, et al., AIP Publication, there are proposed serrated strips of Permalloy film, about 350 A in thickness and 10 microns (.mu.m) in width, which serrated strips are etched from a planar layer of magnetic material so that the strips are aligned along the easy axis of the film. After an external magnetic field is applied normal to the strip length, i.e., transverses the easy axis of the film, the magnetization along the opposing serrated edges rotates back to the nearest direction that is parallel to the edge. This generates two large domains that are separated by a Neel or cross-tie wall that is formed along the centerline of the strip. Cross-ties are energetically more stable at the energy wells formed by the necks or narrow portions of the serrated strips, while Bloch-lines are energetically more stable at the energy wells formed by the wide portions between adjacent necks, or narrow portions.
In the G. J. Cosimini, et al., patent application, Ser. No. 20,762, filed Feb. 23, 1979, now U.S. Pat. No. 4,250,565, the disclosure of which is herein incorporated by reference, there is disclosed a cross-tie wall memory system that is comprised of a shift register for shifting cross-tie, Bloch-line pairs therealong through a plurality of memory cells consisting of a transfer section and a store section. The shift register is terminated on one end by a cross-tie, Bloch-line pair generator, for selectively coupling cross-tie, Bloch-line pairs to the shift register, and on the other end by a detector for detecting when a cross-tie has been entered therein from the shift register.
The generator/shift register/detector assembly of G. J. Cosimini, et al., is fabricated in three superposed layers: a straight-edged current conductive strip line; a serrated-edged thin magnetic layer that forms the data track along the geometric centerline of which is formed and structured the cross-tie wall, and a wide-narrow-edged current conductive strip line comprised of a plurality of rectangularly shaped wide portions that are serially coupled by narrow portions therebetween that is terminated on one end by a cross-tie, Bloch-line pair generator and on the other end by a cross-tie detector. Electronic circuitry controls the current drive signals to the straight-edged strip line and/or the wide-narrow-edged strip line to generate the necessary fields for the propagation of the cross-tie, Bloch-line pairs along the serrated-edged data track, to the generator to selectively generate, or not, cross-tie, Bloch-line pairs, and to the detector to detect the presence, or not, of a cross-tie, all in synchronism. The present invention is considered to be an improvement of the design of the magnetic data track of G. J. Cosimini, et al.